The methods and substances used heretofore for the measurement of the partial pressure, i.e., concentration, of gases and vapors, for instance, test tube methods do not provide a continuously operating determination method for measuring a particular gas constituent.
Continuous measurement is possible with mass spectrophotometry. However, the determination capabilities and accuracies attainable with such expensive devices are often not necessary.
Known chemically sensitive sensors for the continuous measurement of the partial pressure of gases and vapors that operate with heated helices or metal oxide films can only be used at high temperatures and are only useful for measuring a few gases. Sensors which operate with solid electrolytes or with palladium gate field-effect transistors are useful only for the measurement of oxygen and hydrogen, respectively.